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{{St. Louis encephalitis}}
{{St. Louis encephalitis}}
{{CMG}}; {{AE}} {{AG}}; '''Contributor(s):''' {{VVS}}
{{CMG}}; {{AE}} {{AG}}; '''Contributor(s):''' {{Irfan Dotani}}, {{VVS}}


==Overview==
==Overview==
St. Louis encephalitis is one of the most common mosquito-transmitted human pathogens in the United States. St. Louis encephalitis virus is a flavivirus that was first identified in St. Louis, Missouri in 1933. St. Louis encephalitis is diagnosed based on symptoms, physical findings, laboratory testing, and the possibility of exposure to infected mosquitoes.   There is no specific treatment for St. Louis encephalitis; care is based on symptoms. Steps to prevent infection with St. Louis encephalitis virus include use of insect repellent, protective clothing, and staying indoors while mosquitoes are most active. While periodic St. Louis encephalitis epidemics have occurred only in the Midwest and Southeast, St. Louis encephalitis virus is distributed throughout the lower 48 states
St. Louis encephalitis is a moderate [[infection]] of the [[central nervous system]]. St. Louis encephalitis virus is a Group IV positive-sense ssRNA virus within the ''[[Flaviviridae]]'' family of viruses, and the genus ''[[Flavivirus]]''. St. Louis encephalitis virus is closely related to [[Yellow fever virus]], [[Dengue virus]], [[West Nile virus]], and [[Japanese encephalitis|Japanese encephalitis]].<ref name=ViralZoneFlavi> Flavivirus. SIB Swiss Institute of Bioinformatics (2015). http://viralzone.expasy.org/viralzone/all_by_species/24.html Accessed on April 12, 2016</ref> St. Louis encephalitis is also known as an [[arbovirus]], or an arthropod-borne virus. St. Louis encephalitis is usually transmitted via [[mosquito]]es to the human host. St. Louis encephalitis must be differentiated from other diseases that cause nondescript symptoms, which include [[fever]], [[headache]], and [[vomiting]]. Prognosis is generally poor. Approximately 5-30% of patients progress to [[mortality]]. Among patients who survive, approximately 50% suffer severe [[neurological]], [[cognitive]], and [[psychological]] deficits.<ref name="pmid22993280">{{cite journal| author=Khandaker G, Zurynski Y, Buttery J, Marshall H, Richmond PC, Dale RC et al.| title=Neurologic complications of influenza A(H1N1)pdm09: surveillance in 6 pediatric hospitals. | journal=Neurology | year= 2012 | volume= 79 | issue= 14 | pages= 1474-81 | pmid=22993280 | doi=10.1212/WNL.0b013e31826d5ea7 | pmc=PMC4098823 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22993280  }} </ref> The diagnostic method of choice for St. Louis encephalitis is laboratory testing. Laboratory findings consistent with the diagnosis of [[leukocytosis]], mild [[anemia]], and [[hyponatremia]]. There is no treatment for St. Louis encephalitis; the mainstay of therapy is supportive care.
 
==Historical Perspective==
St. Louis encephalitis was first discovered by Dr. Joseph F. Bredeck, an American Director of Public Health for the City of St. Louis, in 1933 following a major [[outbreak]] in the city. During Autumn of 1933, over 1,000 cases were reported to local health departments and the [[National Institute of Health]].<ref name="pmid18013846">{{cite journal| author=| title=ENCEPHALITIS IN ST. LOUIS. | journal=Am J Public Health Nations Health | year= 1933 | volume= 23 | issue= 10 | pages= 1058-60 | pmid=18013846 | doi= | pmc=PMC1558319 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18013846  }} </ref> The previously unknown virus that caused the epidemic was isolated by the NIH team first in monkeys and then in white mice.<ref name="pmid21629729">{{cite journal| author=Diaz LA, Nemeth NM, Bowen RA, Almiron WR, Contigiani MS| title=Comparison of argentinean saint louis encephalitis virus non-epidemic and epidemic strain infections in an avian model. | journal=PLoS Negl Trop Dis | year= 2011 | volume= 5 | issue= 5 | pages= e1177 | pmid=21629729 | doi=10.1371/journal.pntd.0001177 | pmc=3101189 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21629729  }} </ref>
 
==Classification==
St. Louis encephalitis may be classified according to location of the disease into 2 subtypes: systemic or encephalitic.<ref name= SLEV>Saint Louis Encephalitis Virus (SLEV). Wisonsin Department of Health Services (2015). https://www.dhs.wisconsin.gov/arboviral/stlouisencephalitis.htm Accessed on July 28, 2016.</ref> St. Louis encephalitis may also be classified according to [[invasive|neuroinvasiveness]] of the disease into two subtypes: neuroinvasive and non-neuroinvasive. St. Louis encephalitis virus is a Group IV positive-sense ssRNA virus within the ''[[Flaviviridae]]'' family of viruses, and the genus ''[[Flavivirus]]''. St. Louis encephalitis is also known as an [[arbovirus]], or an arthopod-borne virus.<ref name="pmid18632961">{{cite journal| author=May FJ, Li L, Zhang S, Guzman H, Beasley DW, Tesh RB et al.| title=Genetic variation of St. Louis encephalitis virus. | journal=J Gen Virol | year= 2008 | volume= 89 | issue= Pt 8 | pages= 1901-10 | pmid=18632961 | doi=10.1099/vir.0.2008/000190-0 | pmc=2696384 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18632961  }} </ref>
 
==Pathophysiology==
St. Louis encephalitis virus is usually transmitted via [[mosquito]]s (generally from the genus ''[[Culex]]'') to the human host. St. Louis encephalitis virus contains [[positive-sense ssRNA virus|positive-sense]] viral [[RNA]]. Transmission to humans requires mosquito species capable of creating a "bridge" between infected animals and uninfected humans. The [[incubation period]] is 5-15 days. Humans are dead-end hosts for the virus, meaning there is an insufficient amount of St. Louis encephalitis virus in the blood stream to infect a mosquito; there is also no evidence of person to person spread.<ref name=CDCSLEVTransmis> Saint Louis Encephalitis Transmission. Centers for Disease Control and Prevention (CDC), National Center for Emerging and Zoonotic Infectious Diseases, Division of Vector-Borne Diseases. (2010) http://www.cdc.gov/sle/technical/transmission.html Accessed on May 3, 2016. </ref>


==Causes==
==Causes==
St. Louis encephalitis virus is a member of the genus Flavivirus, family Flaviviridae.  Other similar diseases are West Nile virus, eastern equine encephalitis, western equine encephalitis, and La Crosse encephalitis. SLEV has a single-stranded, positive-sense RNA genome. The virus particles are spherical and have a diameter of 40 nm.
St. Louis encephalitis may be caused by St. Louis encephalitis virus. St. Louis encephalitis virus is closely related to the [[West Nile virus]], [[Dengue virus]], [[Murray Valley encephalitis virus]], and [[Japanese encephalitis]] virus.<ref name="pmid27473856">{{cite journal| author=Rastogi M, Sharma N, Singh SK| title=Flavivirus NS1: a multifaceted enigmatic viral protein. | journal=Virol J | year= 2016 | volume= 13 | issue= 1 | pages= 131 | pmid=27473856 | doi=10.1186/s12985-016-0590-7 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=27473856  }} </ref>


==Differentiating St. Louis encephalitis from other Diseases==
==Differentiating St. Louis encephalitis from other Diseases==
St. Louis encephalitis virus is a member of the genus Flavivirus, family Flaviviridae. Other similar diseases are West Nile virus, eastern equine encephalitis, western equine encephalitis, and La Crosse encephalitis.
St. Louis encephalitis must be differentiated from other diseases that cause nondescript symptoms, which include [[fever]], [[headache]], [[myalgia]], and [[vomiting]], such as [[meningitis]], [[brain abscess]], and [[demyelinating disease]]s.<ref name="pmid24490165">{{cite journal| author=Burgueño A, Spinsanti L, Díaz LA, Rivarola ME, Arbiza J, Contigiani M et al.| title=Seroprevalence of St. Louis encephalitis virus and West Nile virus (Flavivirus, Flaviviridae) in horses, Uruguay. | journal=Biomed Res Int | year= 2013 | volume= 2013 | issue=  | pages= 582957 | pmid=24490165 | doi=10.1155/2013/582957 | pmc=3891745 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24490165  }} </ref>


==Epidemiology and Demographics==
==Epidemiology and Demographics==
4,651 cases have been reported throughout the United States from 1964 to 2005. Over this time period, the central and eastern states have reported the largest number of cases. In temperate areas of the United States, St. Louis encephalitis cases occur primarily in the late summer or early fall. In the southern states, where the climate is milder, St. Louis encephalitis can occur year round.
The [[incidence]] of St. Louis encephalitis is approximately 192 per 100,000 individuals worldwide. The majority of St. Louis encephalitis cases are reported in the United States. In the United States, the annual number of reported St. Louis encephalitis cases reported fluctuate widely, as a result of periodic [[epidemics]]. St. Louis encephalitis infection is thought to confer lifelong immunity against reinfection. The case fatality rate of St. Louis encephalitis ranges between 5-30%, with higher rates among the [[elderly]], worldwide. St. Louis encephalitis affects men and women equally. There is no racial predilection to the development of St. Louis encephalitis. Patients of all age groups may develop St. Louis encephalitis.<ref name="pmid6109458">{{cite journal| author=Bell RL, Christensen B, Holguin A, Smith O| title=St. Louis encephalitis: a comparison of two epidemics in Harris county, Texas. | journal=Am J Public Health | year= 1981 | volume= 71 | issue= 2 | pages= 168-70 | pmid=6109458 | doi= | pmc=1619618 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6109458  }} </ref>


==Risk Factors==
==Risk Factors==
All residents of and visitors to areas where SLEV activity has been identified are at risk of SLEV infection, particularly persons who engage in outdoor work and recreational activities and those living in low-income areas. SLEV infection is thought to confer life-long immunity against re-infection with SLEV. The elderly are at highest risk for severe disease and death.
The most potent risk factor in the development of St. Louis encephalitis is [[old age]]. Common risk factors include [[immunosuppression]], [[mosquito]] contact, and visits to Central and South America.<ref name= SLEVPSD>ST. LOUIS ENCEPHALITIS VIRUS. Public Health Agency of Canada(2011). http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/st-louis-encephalit-eng.php Accessed on August 1, 2016.</ref>
 
==Screening==
According to the Centers for Disease Control and Prevention, there is insufficient evidence to recommend routine screening for St. Louis encephalitis.<ref name=CDCJapEnceph1> Japanese encephalitis - Frequently Asked Questions. CDC Centers for Disease Control and Prevention. (2015) http://www.cdc.gov/japaneseencephalitis/qa/index.html Accessed on April 12, 2016</ref>


==Natural History, Complications and Prognosis==
==Natural History, Complications and Prognosis==
Mortality rate ranges from 5% to 30%, with higher rates among the elderly.
If left untreated, approxomatly 40% of patients with St. Louis encephalitis may progress to develop fever, headache, or aseptic meningitis.<ref name=SLE>Saint Louis Encephalitis. Centers for Disease Control, and Prevention (2010). https://www.cdc.gov/sle/technical/symptoms.html Accessed on July 29, 2016.</ref> Common complications of St. Louis encephalitis include [[seizures]], [[coma]], [[disorientation]], [[spastic paralysis]], and [[hemorrhage]].<ref name=FESLEV>Flavivirus encephalitis. Radiopaedia.org (2015). http://radiopaedia.org/articles/flavivirus-encephalitis Accessed on July 29, 2016.</ref> Prognosis is generally poor. Approximately 5-15% of patients progress to [[mortality]]. Among patients who survive, approximately 50% suffer severe [[neurological]], [[cognitive]], or [[psychological]] deficits.


==Diagnosis==
==Diagnosis==
===History and Symptoms===
If possible, a detailed and thorough history from the patient is necessary. Most patients infected with St. Louis encephalitis remain [[asymptomatic]]. Less than 1% of St. Louis encephalitis infections are clinically apparent and the vast majority of infections remain undiagnosed.<ref name=SLEV>Saint Louis Encephalitis. Centers for Disease Control and Prevention (2009). https://www.cdc.gov/sle/technical/symptoms.html Accessed on July 29, 2016.</ref> The [[incubation period]] for St. Louis encephalitis is usually 5-15 days. Common symptoms of St. Louis encephalitis include [[fever]], [[headache]], and [[dizziness]].<ref name="pmid27399031">{{cite journal| author=Carballo C, Cabana M, Ledezma F, Pascual C, Cazes C, Mistchenko A et al.| title=[Saint Louis encephalitis: case report]. | journal=Arch Argent Pediatr | year= 2016 | volume= 114 | issue= 4 | pages= e268-71 | pmid=27399031 | doi=10.5546/aap.2016.e268 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=27399031  }} </ref>


In acute SLEV neuroinvasive disease cases, cerebrospinal fluid (CSF) examination shows a moderate (typically lymphocytic) pleocytosis. CSF protein is elevated in about a half to two-thirds of cases. Computed tomography (CT) brain scans are usually normal; electroencephalographic (EEG) results often show generalized slowing without focal activity.
===Physical Examination===
Patients with St. Louis encephalitis are usually ill-appearing. Physical examination of patients with St. Louis encephalitis is usually remarkable for [[fever]], [[convulsions]], and [[hemorrhage]].<ref name=SLE>Saint Louis Encephalitis. Centers for Disease Prevention and Control (2009). https://www.cdc.gov/sle/technical/fact.html Accessed on August 1, 2016.</ref><ref name="pmid27399031">{{cite journal| author=Carballo C, Cabana M, Ledezma F, Pascual C, Cazes C, Mistchenko A et al.| title=[Saint Louis encephalitis: case report]. | journal=Arch Argent Pediatr | year= 2016 | volume= 114 | issue= 4 | pages= e268-71 | pmid=27399031 | doi=10.5546/aap.2016.e268 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=27399031  }} </ref>


SLEV is difficult to isolate from clinical samples and almost all isolates have come from brain tissue or CSF. In the absence of a sensitive and non-invasive virus detection method, serologic testing is the primary method for diagnosing SLEV infection. Combined with a consistent clinico-epidemiologic presentation, a rapid and accurate diagnosis of acute neuroinvasive SLEV disease can be made by the detection of SLEV-specific IgM antibody in serum or CSF. SLEV IgM tests are available commercially, in some state health department laboratories, and at CDC. A positive SLEV IgM test result should be confirmed by neutralizing antibody testing of acute- and convalescent-phase serum specimens at a state public health laboratory or CDC. To submit specimens for testing at CDC, contact your state health department. All SLEV disease cases should be reported to local public health authorities.
===History and Symptoms===
Less than 1% of St. Louis encephalitis virus (SLEV) infections are clinically apparent and the vast majority of infections remain undiagnosed. The incubation period for SLEV disease (the time from infected mosquito bite to onset of illness) ranges from 5 to 15 days. Onset of illness is usually abrupt, with [[fever]], [[headache]], [[dizziness]], [[nausea]], and [[malaise]]. Signs and symptoms intensify over a period of several days to a week. Some patients spontaneously recover after this period; others develop signs of central nervous system infections, including [[stiff neck]], [[confusion]], [[disorientation]], [[dizziness]], [[tremors]] and [[unsteadiness]]. Coma can develop in severe cases. The disease is generally milder in children than in older adults. About 40% of children and young adults with SLEV disease develop only [[fever]] and [[headache]] or [[aseptic meningitis]]; almost 90% of elderly persons with SLEV disease develop [[encephalitis]]. The overall case-fatality ratio is 5 to 15%. The risk of fatal disease also increases with age.
===Laboratory Findings===
===Laboratory Findings===
In acute SLEV neuroinvasive disease cases, cerebrospinal fluid (CSF) examination shows a moderate (typically lymphocytic) pleocytosis. CSF protein is elevated in about a half to two-thirds of cases.
The diagnostic method of choice for St. Louis encephalitis is laboratory testing. In St. Louis encephalitis, [[cerebrospinal fluid]] examination shows a moderate (typically [[lymphocytic]]) [[pleocytosis]]. 2/3 of patients with St. Louis encephalitis may have elevated concentration of CSF protein, which usually indicative of neuroinvasive disease. In the absence of a sensitive and non-invasive virus detection method, serologic testing is the primary method for diagnosing St. Louis encephalitis.<ref name= SLEV>Saint Louis Encephalitis. Centers for Disease Prevention and Control (2009). https://www.cdc.gov/sle/technical/symptoms.html Accessed on August 1, 2016.</ref><ref name= SLE>St. Louis Encephalitis Virus Antibodies (IgG, IgM). Quest Diagnostics (2016). http://www.questdiagnostics.com/testcenter/BUOrderInfo.action?tc=34982X&labCode=QTE Accessed on August 1, 2016.</ref><ref name="pmid19960704">{{cite journal| author=Day JF, Shaman J| title=Severe winter freezes enhance St. Louis encephalitis virus amplification and epidemic transmission in peninsular Florida. | journal=J Med Entomol | year= 2009 | volume= 46 | issue= 6 | pages= 1498-506 | pmid=19960704 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19960704  }} </ref>
 
===Imaging Findings===
====Electrocardiogram====
There are no electrocardiogram findings associated with St. Louis encephalitis.
 
====X Ray====
There are no x ray findings associated with St. Louis encephalitis.
 
====CT====
There are no CT findings associated with St. Louis encephalitis.<ref name=AJNRCT>Brain Imaging. American Journal of Neuroradiology(2016). http://www.ajnr.org/content/20/7/1281.full Accessed on July 27, 2016</ref><ref name=SLEVRP>Flavivirus encephalitis. Radiopaedia.org(2015).http://radiopaedia.org/articles/flavivirus-encephalitis Accessed on July 27, 2016</ref>
 
====MRI====
[[MRI]] is the imaging modality of choice for St. Louis encephalitis. Findings of St. Louis encephalitis include [[substantia nigra]] edema, [[hemorrhage]], and restricted diffusion in the [[basal ganglia]] and [[thalamus]].<ref name=SLEVRP>Flavivirus encephalitis. Radiopaedia.org (2015).http://radiopaedia.org/articles/flavivirus-encephalitis Accessed on July 27, 2016</ref><ref name=SLEVCR>St. Louis Encephalitis and the Substantia Nigra: MR Imaging Evaluation.(1999). http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.321.6020&rep=rep1&type=pdf Accessed on July 27, 2016</ref><ref name="pmid10634457">{{cite journal| author=Wasay M, Diaz-Arrastia R, Suss RA, Kojan S, Haq A, Burns D et al.| title=St Louis encephalitis: a review of 11 cases in a 1995 Dallas, Tex, epidemic. | journal=Arch Neurol | year= 2000 | volume= 57 | issue= 1 | pages= 114-8 | pmid=10634457 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10634457  }} </ref>
 
====Echocardiography or Ultrasound====
There are no echocardiography or ultrasound findings associated with St. Louis encephalitis.<ref name=IDUS>Mandell, Douglas, and Bennett's Principles and Practice of Infectious Disease. (2015). Accessed on July 27, 2016</ref>
 
====EEG====
On other imaging findings, St. Louis encephalitis is characterized by generalized slowing without focal activity, a [[persistent vegetative state]], and [[brain death]].<ref name="pmid27226371">{{cite journal| author=Zhao J, Vijay R, Zhao J, Gale M, Diamond MS, Perlman S| title=MAVS Expressed by Hematopoietic Cells Is Critical for Control of West Nile Virus Infection and Pathogenesis. | journal=J Virol | year= 2016 | volume= 90 | issue= 16 | pages= 7098-108 | pmid=27226371 | doi=10.1128/JVI.00707-16 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=27226371  }} </ref>
 
===Other Diagnostic Studies===
[[Ultrasound]]-guided [[Needle aspiration biopsy|aspiration]], via transdural insonation, has proven to show excellent [[abscess]] visualization when performed through a [[burr hole]].
 
At the time of [[Needle aspiration biopsy|aspiration]], specimens should be sent for [[Gram stain]] and routine [[aerobic]] and [[anaerobic]] cultures.<ref name=IDSLEV>John E. Bennett, Raphael Dolin, Martin J. Blaser "Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases" (2014): 1171.</ref>


===CT===
Computed tomography (CT) brain scans are usually normal.
==Treatment==
==Treatment==
No vaccine against SLEV infection or specific antiviral treatment for clinical SLEV infections is available. Patients with suspected SLE should be evaluated by a healthcare provider, appropriate serologic and other diagnostic tests ordered, and supportive treatment provided.
===Medical Therapy===
There is no treatment for St. Louis encephalitis; the mainstay of therapy for St. Louis encephalitis is supportive care.<ref name=SLEV>Saint Louis Encephalitis. Centers for Disease Control and Prevention (2009). http://www.cdc.gov/sle/technical/symptoms.html Accessed on August 1, 2016.</ref><ref name=SLE> Saint Louis Encephalitis. Centers for Disease Control and Prevention (2010). https://www.cdc.gov/sle/general/qa.html#treatment Accessed on August 1, 2016.</ref>
 
===Surgery===
Surgical intervention is not recommended for the management of St. Louis encephalitis.
 
===Primary Prevention===
There are no available vaccines against St. Louis encephalitis virus. Primary prevention strategies include the use of repellent, protective clothing, window screens, and the reduction of uncontrolled mosquito populations.<ref name=CDCJapEnceph1> Japanese encephalitis - Frequently Asked Questions. CDC Centers for Disease Control and Prevention. (2015) http://www.cdc.gov/japaneseencephalitis/qa/index.html Accessed on April 12, 2016</ref><ref name="pmid26912625">{{cite journal| author=McAuley AJ, Torres M, Plante JA, Huang CY, Bente DA, Beasley DW| title=Recovery of West Nile Virus Envelope Protein Domain III Chimeras with Altered Antigenicity and Mouse Virulence. | journal=J Virol | year= 2016 | volume= 90 | issue= 9 | pages= 4757-70 | pmid=26912625 | doi=10.1128/JVI.02861-15 | pmc=4836310 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=26912625  }} </ref>
 
===Secondary Prevention===
There are no secondary preventative measures available for St. Louis encephalitis.<ref name=CDCJapEnceph1> Japanese encephalitis - Frequently Asked Questions. CDC Centers for Disease Control and Prevention. (2015) http://www.cdc.gov/japaneseencephalitis/qa/index.html Accessed on April 12, 2016</ref>


==References==
==References==
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{{reflist|2}}


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Latest revision as of 19:07, 18 September 2017

St. Louis encephalitis Microchapters

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]; Contributor(s): Irfan Dotani [3], Vishnu Vardhan Serla M.B.B.S. [4]

Overview

St. Louis encephalitis is a moderate infection of the central nervous system. St. Louis encephalitis virus is a Group IV positive-sense ssRNA virus within the Flaviviridae family of viruses, and the genus Flavivirus. St. Louis encephalitis virus is closely related to Yellow fever virus, Dengue virus, West Nile virus, and Japanese encephalitis.[1] St. Louis encephalitis is also known as an arbovirus, or an arthropod-borne virus. St. Louis encephalitis is usually transmitted via mosquitoes to the human host. St. Louis encephalitis must be differentiated from other diseases that cause nondescript symptoms, which include fever, headache, and vomiting. Prognosis is generally poor. Approximately 5-30% of patients progress to mortality. Among patients who survive, approximately 50% suffer severe neurological, cognitive, and psychological deficits.[2] The diagnostic method of choice for St. Louis encephalitis is laboratory testing. Laboratory findings consistent with the diagnosis of leukocytosis, mild anemia, and hyponatremia. There is no treatment for St. Louis encephalitis; the mainstay of therapy is supportive care.

Historical Perspective

St. Louis encephalitis was first discovered by Dr. Joseph F. Bredeck, an American Director of Public Health for the City of St. Louis, in 1933 following a major outbreak in the city. During Autumn of 1933, over 1,000 cases were reported to local health departments and the National Institute of Health.[3] The previously unknown virus that caused the epidemic was isolated by the NIH team first in monkeys and then in white mice.[4]

Classification

St. Louis encephalitis may be classified according to location of the disease into 2 subtypes: systemic or encephalitic.[5] St. Louis encephalitis may also be classified according to neuroinvasiveness of the disease into two subtypes: neuroinvasive and non-neuroinvasive. St. Louis encephalitis virus is a Group IV positive-sense ssRNA virus within the Flaviviridae family of viruses, and the genus Flavivirus. St. Louis encephalitis is also known as an arbovirus, or an arthopod-borne virus.[6]

Pathophysiology

St. Louis encephalitis virus is usually transmitted via mosquitos (generally from the genus Culex) to the human host. St. Louis encephalitis virus contains positive-sense viral RNA. Transmission to humans requires mosquito species capable of creating a "bridge" between infected animals and uninfected humans. The incubation period is 5-15 days. Humans are dead-end hosts for the virus, meaning there is an insufficient amount of St. Louis encephalitis virus in the blood stream to infect a mosquito; there is also no evidence of person to person spread.[7]

Causes

St. Louis encephalitis may be caused by St. Louis encephalitis virus. St. Louis encephalitis virus is closely related to the West Nile virus, Dengue virus, Murray Valley encephalitis virus, and Japanese encephalitis virus.[8]

Differentiating St. Louis encephalitis from other Diseases

St. Louis encephalitis must be differentiated from other diseases that cause nondescript symptoms, which include fever, headache, myalgia, and vomiting, such as meningitis, brain abscess, and demyelinating diseases.[9]

Epidemiology and Demographics

The incidence of St. Louis encephalitis is approximately 192 per 100,000 individuals worldwide. The majority of St. Louis encephalitis cases are reported in the United States. In the United States, the annual number of reported St. Louis encephalitis cases reported fluctuate widely, as a result of periodic epidemics. St. Louis encephalitis infection is thought to confer lifelong immunity against reinfection. The case fatality rate of St. Louis encephalitis ranges between 5-30%, with higher rates among the elderly, worldwide. St. Louis encephalitis affects men and women equally. There is no racial predilection to the development of St. Louis encephalitis. Patients of all age groups may develop St. Louis encephalitis.[10]

Risk Factors

The most potent risk factor in the development of St. Louis encephalitis is old age. Common risk factors include immunosuppression, mosquito contact, and visits to Central and South America.[11]

Screening

According to the Centers for Disease Control and Prevention, there is insufficient evidence to recommend routine screening for St. Louis encephalitis.[12]

Natural History, Complications and Prognosis

If left untreated, approxomatly 40% of patients with St. Louis encephalitis may progress to develop fever, headache, or aseptic meningitis.[13] Common complications of St. Louis encephalitis include seizures, coma, disorientation, spastic paralysis, and hemorrhage.[14] Prognosis is generally poor. Approximately 5-15% of patients progress to mortality. Among patients who survive, approximately 50% suffer severe neurological, cognitive, or psychological deficits.

Diagnosis

History and Symptoms

If possible, a detailed and thorough history from the patient is necessary. Most patients infected with St. Louis encephalitis remain asymptomatic. Less than 1% of St. Louis encephalitis infections are clinically apparent and the vast majority of infections remain undiagnosed.[5] The incubation period for St. Louis encephalitis is usually 5-15 days. Common symptoms of St. Louis encephalitis include fever, headache, and dizziness.[15]

Physical Examination

Patients with St. Louis encephalitis are usually ill-appearing. Physical examination of patients with St. Louis encephalitis is usually remarkable for fever, convulsions, and hemorrhage.[13][15]

Laboratory Findings

The diagnostic method of choice for St. Louis encephalitis is laboratory testing. In St. Louis encephalitis, cerebrospinal fluid examination shows a moderate (typically lymphocytic) pleocytosis. 2/3 of patients with St. Louis encephalitis may have elevated concentration of CSF protein, which usually indicative of neuroinvasive disease. In the absence of a sensitive and non-invasive virus detection method, serologic testing is the primary method for diagnosing St. Louis encephalitis.[5][13][16]

Imaging Findings

Electrocardiogram

There are no electrocardiogram findings associated with St. Louis encephalitis.

X Ray

There are no x ray findings associated with St. Louis encephalitis.

CT

There are no CT findings associated with St. Louis encephalitis.[17][18]

MRI

MRI is the imaging modality of choice for St. Louis encephalitis. Findings of St. Louis encephalitis include substantia nigra edema, hemorrhage, and restricted diffusion in the basal ganglia and thalamus.[18][19][20]

Echocardiography or Ultrasound

There are no echocardiography or ultrasound findings associated with St. Louis encephalitis.[21]

EEG

On other imaging findings, St. Louis encephalitis is characterized by generalized slowing without focal activity, a persistent vegetative state, and brain death.[22]

Other Diagnostic Studies

Ultrasound-guided aspiration, via transdural insonation, has proven to show excellent abscess visualization when performed through a burr hole.

At the time of aspiration, specimens should be sent for Gram stain and routine aerobic and anaerobic cultures.[23]

Treatment

Medical Therapy

There is no treatment for St. Louis encephalitis; the mainstay of therapy for St. Louis encephalitis is supportive care.[5][13]

Surgery

Surgical intervention is not recommended for the management of St. Louis encephalitis.

Primary Prevention

There are no available vaccines against St. Louis encephalitis virus. Primary prevention strategies include the use of repellent, protective clothing, window screens, and the reduction of uncontrolled mosquito populations.[12][24]

Secondary Prevention

There are no secondary preventative measures available for St. Louis encephalitis.[12]

References

  1. ↑ Flavivirus. SIB Swiss Institute of Bioinformatics (2015). http://viralzone.expasy.org/viralzone/all_by_species/24.html Accessed on April 12, 2016
  2. ↑ Khandaker G, Zurynski Y, Buttery J, Marshall H, Richmond PC, Dale RC; et al. (2012). "Neurologic complications of influenza A(H1N1)pdm09: surveillance in 6 pediatric hospitals". Neurology. 79 (14): 1474–81. doi:10.1212/WNL.0b013e31826d5ea7. PMC 4098823. PMID 22993280.
  3. ↑ "ENCEPHALITIS IN ST. LOUIS". Am J Public Health Nations Health. 23 (10): 1058–60. 1933. PMC 1558319. PMID 18013846.
  4. ↑ Diaz LA, Nemeth NM, Bowen RA, Almiron WR, Contigiani MS (2011). "Comparison of argentinean saint louis encephalitis virus non-epidemic and epidemic strain infections in an avian model". PLoS Negl Trop Dis. 5 (5): e1177. doi:10.1371/journal.pntd.0001177. PMC 3101189. PMID 21629729.
  5. ↑ 5.0 5.1 5.2 5.3 Saint Louis Encephalitis Virus (SLEV). Wisonsin Department of Health Services (2015). https://www.dhs.wisconsin.gov/arboviral/stlouisencephalitis.htm Accessed on July 28, 2016.
  6. ↑ May FJ, Li L, Zhang S, Guzman H, Beasley DW, Tesh RB; et al. (2008). "Genetic variation of St. Louis encephalitis virus". J Gen Virol. 89 (Pt 8): 1901–10. doi:10.1099/vir.0.2008/000190-0. PMC 2696384. PMID 18632961.
  7. ↑ Saint Louis Encephalitis Transmission. Centers for Disease Control and Prevention (CDC), National Center for Emerging and Zoonotic Infectious Diseases, Division of Vector-Borne Diseases. (2010) http://www.cdc.gov/sle/technical/transmission.html Accessed on May 3, 2016.
  8. ↑ Rastogi M, Sharma N, Singh SK (2016). "Flavivirus NS1: a multifaceted enigmatic viral protein". Virol J. 13 (1): 131. doi:10.1186/s12985-016-0590-7. PMID 27473856.
  9. ↑ Burgueño A, Spinsanti L, Díaz LA, Rivarola ME, Arbiza J, Contigiani M; et al. (2013). "Seroprevalence of St. Louis encephalitis virus and West Nile virus (Flavivirus, Flaviviridae) in horses, Uruguay". Biomed Res Int. 2013: 582957. doi:10.1155/2013/582957. PMC 3891745. PMID 24490165.
  10. ↑ Bell RL, Christensen B, Holguin A, Smith O (1981). "St. Louis encephalitis: a comparison of two epidemics in Harris county, Texas". Am J Public Health. 71 (2): 168–70. PMC 1619618. PMID 6109458.
  11. ↑ ST. LOUIS ENCEPHALITIS VIRUS. Public Health Agency of Canada(2011). http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/st-louis-encephalit-eng.php Accessed on August 1, 2016.
  12. ↑ 12.0 12.1 12.2 Japanese encephalitis - Frequently Asked Questions. CDC Centers for Disease Control and Prevention. (2015) http://www.cdc.gov/japaneseencephalitis/qa/index.html Accessed on April 12, 2016
  13. ↑ 13.0 13.1 13.2 13.3 Saint Louis Encephalitis. Centers for Disease Control, and Prevention (2010). https://www.cdc.gov/sle/technical/symptoms.html Accessed on July 29, 2016.
  14. ↑ Flavivirus encephalitis. Radiopaedia.org (2015). http://radiopaedia.org/articles/flavivirus-encephalitis Accessed on July 29, 2016.
  15. ↑ 15.0 15.1 Carballo C, Cabana M, Ledezma F, Pascual C, Cazes C, Mistchenko A; et al. (2016). "[Saint Louis encephalitis: case report]". Arch Argent Pediatr. 114 (4): e268–71. doi:10.5546/aap.2016.e268. PMID 27399031.
  16. ↑ Day JF, Shaman J (2009). "Severe winter freezes enhance St. Louis encephalitis virus amplification and epidemic transmission in peninsular Florida". J Med Entomol. 46 (6): 1498–506. PMID 19960704.
  17. ↑ Brain Imaging. American Journal of Neuroradiology(2016). http://www.ajnr.org/content/20/7/1281.full Accessed on July 27, 2016
  18. ↑ 18.0 18.1 Flavivirus encephalitis. Radiopaedia.org(2015).http://radiopaedia.org/articles/flavivirus-encephalitis Accessed on July 27, 2016
  19. ↑ St. Louis Encephalitis and the Substantia Nigra: MR Imaging Evaluation.(1999). http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.321.6020&rep=rep1&type=pdf Accessed on July 27, 2016
  20. ↑ Wasay M, Diaz-Arrastia R, Suss RA, Kojan S, Haq A, Burns D; et al. (2000). "St Louis encephalitis: a review of 11 cases in a 1995 Dallas, Tex, epidemic". Arch Neurol. 57 (1): 114–8. PMID 10634457.
  21. ↑ Mandell, Douglas, and Bennett's Principles and Practice of Infectious Disease. (2015). Accessed on July 27, 2016
  22. ↑ Zhao J, Vijay R, Zhao J, Gale M, Diamond MS, Perlman S (2016). "MAVS Expressed by Hematopoietic Cells Is Critical for Control of West Nile Virus Infection and Pathogenesis". J Virol. 90 (16): 7098–108. doi:10.1128/JVI.00707-16. PMID 27226371.
  23. ↑ John E. Bennett, Raphael Dolin, Martin J. Blaser "Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases" (2014): 1171.
  24. ↑ McAuley AJ, Torres M, Plante JA, Huang CY, Bente DA, Beasley DW (2016). "Recovery of West Nile Virus Envelope Protein Domain III Chimeras with Altered Antigenicity and Mouse Virulence". J Virol. 90 (9): 4757–70. doi:10.1128/JVI.02861-15. PMC 4836310. PMID 26912625.


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